@misc{Lledo1999,
  author    = {Lled{\´o}, Fernando},
  title     = {Contributions to operator theory in spaces with an indefinite metric, the Heinz Langer anniversary volume, A. S. Dijksma ... eds.; Basel [u.a.], Birkh{\"a}user, 1998, ISBN 3-7643-6003-8},
  year      = {1999},
  language  = {en}
}
@misc{Schmidt1999,
  author    = {Schmidt, Hans-J{\"u}rgen},
  title     = {Cercignani, C., Scaling limits and models in physical process; Basel, Birkh{\"a}user, 1998},
  year      = {1999},
  language  = {en}
}
@misc{Schrohe1999,
  author    = {Schrohe, Elmar},
  title     = {Lesch, M., Operators of Fuchs type, conical singularities, and asymptotic methods},
  year      = {1999},
  language  = {en}
}